title: Ultrafast evolution of the excited states in the chlorophyll a/b complex CP29 from green plants studied by energy-selective pump-probe spectroscopy.
abstract: The energy transfer process in the minor light-harvesting antenna complex CP29 of green plants was probed in multicolor transient absorption experiments at 77 K using selective subpicosecond excitation pulses at 640 and 650 nm. Energy flow from each of the chlorophyll (Chl) b molecules of the complex could thus be studied separately. The analysis of our data showed that the "blue" Chl b (absorption around 640 nm) transfers excitation to a "red" Chl a with a time constant of 350 +/- 100 fs, while the 'red' Chl b (absorption at 650 nm) transfers on a picosecond time scale (2.2 +/- 0.5 ps) toward a "blue" Chl a. Furthermore, both fast (280 +/- 50 fs) and slow (10-13 ps) equilibration processes among the Chl a molecules were observed, with rates and associated spectra very similar to those of the major antenna complex, LHC-II. Based on the protein sequence homology between CP29 and LHC-II, a basic modelling of the observed kinetics was performed using the LHC-II structure and the Förster theory of energy transfer. Thus, an assignment for the spectral properties and orientation of the two Chl's b, as well as for their closest Chl a neighbors, is put forward, and a comparison is made with the previous assignments and models for LHC-II and CP29.
authors.affiliation: Department of Physics and Astronomy, Free University of Amsterdam, The Netherlands.
authors.forename: C C
authors.initials: CC
authors.lastname: Gradinaru
authors.forename: A A
authors.initials: AA
authors.lastname: Pascal
authors.forename: F
authors.initials: F
authors.lastname: van Mourik
authors.forename: B
authors.initials: B
authors.lastname: Robert
authors.forename: P
authors.initials: P
authors.lastname: Horton
authors.forename: R
authors.initials: R
authors.lastname: van Grondelle
authors.forename: H
authors.initials: H
authors.lastname: van Amerongen
mesh_terms: D002734:Chlorophyll / Q000378:metabolism* / Q000528:radiation effects; D000077194:Chlorophyll A; D004735:Energy Transfer; D007834:Lasers; D008027:Light; D045342:Light-Harvesting Protein Complexes; D008956:Models, Chemical; D008958:Models, Molecular; D045322:Photosynthetic Reaction Center Complex Proteins / Q000302:isolation & purification / Q000378:metabolism* / Q000528:radiation effects; D045332:Photosystem II Protein Complex; D013053:Spectrophotometry; D018724:Spinacia oleracea; D013997:Time Factors
chemical_list: C069660:CP29 light harvesting complex; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; C037184:chlorophyll b; D000077194:Chlorophyll A